1. Field of the Invention
The present invention relates generally to an electrolytic capacitor that can be built in a board, for use in a high-speed power source circuit, to a circuit board containing an electrolytic capacitor, and to a method for producing the same.
2. Related Background Art
Conventionally, an electrolytic capacitor in which a valve metal such as aluminum or tantalum is used, and a multilayered ceramic capacitor in which Ag/Pd or Ni is used for electrodes and barium titanate is used as a dielectric, have been known as capacitors. These capacitors are used in many power source circuits. Recently, since CPU driving circuits and switching power source circuits particularly are required to be driven with a lower driving voltage, to consume less power, and to be fitted for high frequencies, a capacitor also is required to have a large capacitance, a low equivalent series resistance (hereinafter referred to as ESR), and a low equivalent series inductance (hereinafter referred to as ESL). To meet with these requirements, particularly for a capacitor to have a low ESR, a technique in which a specialty polymer having a high electroconductivity (conductive polymer) is used as a solid electrolyte for a cathode has been examined and developed.
A configuration of a conventional specialty polymer electrolytic capacitor is described below, with reference to FIG. 11. FIG. 11 is a cross-sectional view of a conventional specialty polymer electrolytic capacitor. In FIG. 10, 101 denotes an aluminum foil for an anode (hereinafter referred to as anode-use aluminum foil). 102 denotes a dielectric layer. 103 denotes a conductive polymer layer. 104 denotes a carbon layer. 105 denotes an Ag paste layer. 106 denotes a lead frame. 107 denotes a lead frame. 108 denotes a molding resin.
The anode-use aluminum foil 101 has been treated so as to have rough surfaces, and is provided with the dielectric layer 102 on the surfaces. On the surfaces of the anode-use aluminum foil 101 provided with the dielectric layer 102, the conductive polymer layer 103 made of polypyrrole, polythiophene, polyaniline, etc. is formed. Furthermore, on the conductive polymer layer 103, the carbon layer 104 and the Ag paste layer 105 are formed in the stated order, so that a conventional capacitor unit is provided. Further, the lead frame 106 and the lead frame 107 that function as an anode terminal and as a cathode terminal, respectively, are bonded with the foregoing conventional capacitor unit, and the capacitor unit is sealed with the molding resin 108. Thus, the conventional specialty polymer electrolytic capacitor is formed.
Such a conventional specialty polymer electrolytic capacitor has a lower ESR than that of an electrolytic capacitor using an electrolytic solution as the electrolyte (hereinafter referred to as an electrolytic solution-type electrolytic capacitor). To further increase the capacitance and decrease the ESR, however, a configuration in which a plurality of conventional capacitor units are laminated with an Ag adhesive (Ag adhesive paste) has been developed. Furthermore, as to the foregoing conventional capacitor unit, to decrease the ESR thereof further, materials for the conductive polymer layer 103, the carbon layer 104, and the Ag paste layer 105 have been developed.
Furthermore, recently, the development of capacitors arranged so that not only the ESRs but also the ESLs of the same are reduced for suppression of voltage falling due to inductance components has been needed, for use in high-frequency driving circuits such as MPU power source circuits. Therefore, small-size multilayered ceramic capacitors with small ESLs and electrolytic capacitors with three terminals or four terminals have been developed. Furthermore, circuit boards provided with such capacitors are required to allow LSIs to be driven with high frequencies, in addition to meeting requests for reduction in size and thickness. To obtain such a circuit board, it is necessary to shorten wirings and connections. Therefore, a technique of, for instance, burying a capacitor in a circuit board so as to dispose the capacitor closer to an LSI and thereby reducing inductance components of wirings has been developed.
In the case of the conventional specialty polymer electrolytic capacitor having the aforementioned configuration, however, lead frames are provided as an anode terminal and a cathode terminal, and further, the capacitor unit is larger in size. Therefore, a product of the same has a relatively large size. This makes it difficult to obtain an ESL value lower than 1 nH in the conventional specialty polymer electrolytic capacitor. For this reason, the conventional specialty polymer electrolytic capacitor, whose ESL hardly is reduced despite having a reduced ESR, is inferior to a multilayered ceramic capacitor, which is small in size as a capacitor used in a high-frequency-driven circuit.
On the other hand, as described above, in the case of a high-frequency-driving circuit, which requires the shortening of wirings and connections, a technique of burying a capacitor unit in a circuit board has been developed. However, if the conventional specialty polymer electrolytic capacitor is embedded in the circuit board as it is, serious problems have arisen. Namely, an anode-use valve metal foil having rough surfaces (an etching layer of the anode-use aluminum foil 101 in FIG. 11) and a dielectric (the dielectric layer 102 in FIG. 11) are broken due to stress and the like during a burying operation, thereby causing short circuits to occur and causing leak current to increase. Thus, it has been difficult to obtain sufficient characteristics and reliability by burying the conventional specialty polymer electrolytic capacitor in a circuit board. On the other hand, in the case where a multilayered ceramic capacitor is embedded in a circuit board as well, a drawback is that the multilayered ceramic capacitor is broken due to stress and the like upon a burying operation.
Furthermore, in the case where the conventional specialty polymer electrolytic capacitor is embedded in a circuit board, problems to be solved are present also in the connection of the capacitor with circuit wiring. When a specialty polymer electrolytic capacitor of a conventional lead frame structure is connected with circuit wiring, the lead frame and the circuit wiring are connected by soldering. In this case, the shortening of the connections cannot be achieved, and it is difficult to drive a circuit with a high frequency.
Therefore, with the foregoing in mind, it is an object of the present invention to provide an electrolytic capacitor with a reduced ESL such that the occurrence of short circuits and an increase in leak current can be suppressed when the electrolytic capacitor is embedded in a circuit board, and a method for producing the same, as well as an electrolytic-capacitor-containing circuit board that ensures high-frequency response and large-current driving, and a method for producing the same.
To achieve the foregoing object, an electrolytic capacitor of the present invention includes a valve metal element for an anode including a capacitor forming part and an electrode lead part, a dielectric layer provided on a surface of the valve metal element for an anode, a solid electrolyte layer provided on the dielectric layer, and a charge collecting element for a cathode provided on the solid electrolyte layer. In the electrolytic capacitor, in the valve metal element for an anode, the capacitor forming part and the electrode lead part have a rough surface layer on surfaces thereof, and is compressed in a thickness direction of the rough surface layer.
The electrolytic capacitor is formed using a valve metal element for an anode in a state of being compressed in the thickness direction of the rough surface layer after the surface roughening treatment. Since the valve metal element for an anode is compressed beforehand, it is possible to avoid damage to the rough surface layer of the valve metal element for an anode and to the dielectric layer that is generated due to the stress during a laminating operation, a molding operation, or when the electrolytic capacitor is built in a circuit board. Therefore, it is possible to provide an electrolytic capacitor with high reliability, in which the occurrence of short circuits and an increase in leak current due to stress generated when the electrolytic capacitor is built in a circuit board.
Furthermore, the compression of the valve metal element for anode provides an effect of thinning the capacitor as a whole, thereby ensuring a reduction of the ESL. Furthermore, since it is possible to use the electrode lead part provided in the valve metal element for an anode and the charge collecting element for a cathode as connection terminals, the electrolytic capacitor of the present invention is allowed to have connection terminals for the upper and lower surfaces instead of lead frames. Therefore, this provides reduction of the size of the capacitor as a whole, as well as the shortening of connections in the case where the capacitor is built in a circuit board. Consequently, this ensures further reduction of the ESL, as well as high-frequency driving of a circuit in the case where the capacitor is built in the capacitor.
Furthermore, in the electrolytic capacitor of the present invention, the electrode lead part of the valve metal element for an anode has a rough surface layer on a surface thereof, and is compressed in a thickness direction of the rough surface layer. Therefore, a bulk resistance of the rough surface layer can be lowered in the case where the electrode lead part and circuit wiring are connected electrically. Consequently, this allows resistances upon electric connection with the circuit wiring to be lowered and stabilized, thereby suppressing an increase in the ESR when the capacitor is built in the circuit.
Furthermore, the electrolytic capacitor of the present invention preferably further includes a conductive via hole bored completely through in a thickness direction, and the conductive via hole is provided in a region other than the capacitor forming part, and are insulated electrically from the valve metal element for anode, the solid electrolyte layer, and the charge collecting element for cathode.
This allows electric wiring to pass through the electrolytic capacitor when the electrolytic capacitor is built in a circuit board. Therefore, high densification and high performance can be achieved.
Furthermore, in the electrolytic capacitor of the present invention, a thickness index of the rough surface layer after compression in the capacitor forming part preferably is not less than 0.5 and less than 1.0. Here, the thickness index of the rough surface layer after compression is a thickness of the rough surface layer after compression in the case where a thickness of the rough surface layer before compression is assumed to be 1.
According to the foregoing electrolytic capacitor, the compression provides an effect of an increase in a capacitance.
Furthermore, in the electrolytic capacitor of the present invention, a thickness index of the rough surface layer after compression in the electrode lead part preferably is not more than 0.5. Here, the thickness index of the rough surface layer after compression is as described above.
According to the foregoing electrolytic capacitor, the connection resistance in the case where the capacitor is built in a circuit board can be decreased further.
Furthermore, in the electrolytic capacitor of the present invention, conductive particles preferably are embedded in the electrode lead part so that the conductive particles are exposed on a surface of the electrode lead part. Besides, the conductive particles preferably are selected from the group consisting of Au particles, Ag particles, Cu particles, Ni particles, and C particles.
The foregoing configuration allows further lowering and stabilization of resistances when the electrode lead part and circuit wiring are connected electrically.
Furthermore, in the electrolytic capacitor of the present invention, the charge collecting element for cathode preferably is made of a metal foil in which carbon particles are embedded so that the particles are exposed on a surface of the metal foil.
According to the foregoing electrolytic capacitor, an interface resistance between the charge collecting element for cathode and the solid electrolyte layer is decreased, whereby the ESR is further reduced.
Furthermore, in the electrolytic capacitor of the present invention, the charge collecting element for cathode may be a cladding material, the cladding material including (i) a metal foil in which carbon particles are embedded so that the particles are exposed on a surface of the metal foil, and (ii) a cladding layer.
Furthermore, in the electrolytic capacitor of the present invention, the capacitor forming part and the electrode lead part preferably are provided on a same plane of the valve metal element for an anode.
According to the foregoing electrolytic capacitor, in the case where the electrolytic capacitor of the present embodiment is built in a circuit board, it is possible to obtain lead wires from the anode and the cathode from the same side of the electrolytic capacitor. Therefore, this allows the wiring to be shortened. This allows the electrolytic capacitor to operate sufficiently for high-frequency driving of the circuit.
Furthermore, in the electrolytic capacitor of the present invention, the capacitor forming part may be provided on a first side of the valve metal element for an anode and the electrode lead part may be provided on a second side of the valve metal element for an anode, the second side being opposite to the first side.
Furthermore, in the electrolytic capacitor of the present invention, the valve metal element for anode may include a valve metal layer and a metal layer. Herein the metal layer preferably is made of Cu or Ni.
Furthermore, in the electrolytic capacitor of the present invention, a region other than a predetermined portion of the electrode lead part and a predetermined portion of the charge collecting element for a cathode preferably is sealed with a molding material. Furthermore, by sealing the electrolytic capacitor so that at least one of the electrode lead part and the charge collecting element for a cathode has a plurality of portions uncovered with the molding material, a three-terminal structure or a four-terminal structure can be obtained, whereby the ESL can be decreased further.
To achieve the aforementioned object, a method of the present invention for producing the foregoing electrolytic capacitor includes the steps of roughening at least a surface of a portion of the valve metal element for an anode, the portion being to be the capacitor forming part and the electrode lead part, and compressing the roughened surface portion of the valve metal element for an anode in the thickness direction.
Furthermore, in the electrolytic capacitor producing method of the present invention, the compressing step preferably is carried out so that a thickness index of the rough surface layer after compression in the capacitor forming part is not less than 0.5 and less than 1.0. Here, the thickness index of the rough surface layer after compression is a thickness of the rough surface layer after compression in the case where a thickness of the rough surface layer before compression is assumed to be 1.
Furthermore, in the electrolytic capacitor producing method of the present invention, the compressing step is carried out so that a thickness index of the rough surface layer after compression in the electrode lead part is not more than 0.5. Here, the thickness index of the rough surface layer after compression is as described above.
Furthermore, the electrolytic capacitor producing method of the present invention further may include the step of placing conductive particles on the electrode lead part in a state in which the dielectric layer is formed on a surface of the electrode lead part, and compressing the electrode lead part so that the conductive particles are embedded in the electrode lead part.
Furthermore, the electrolytic capacitor producing method of the present invention preferably further includes the steps of forming the dielectric layer, forming the solid electrolyte layer, and repairing the dielectric layer, wherein the roughening step, the dielectric layer forming step, the solid electrolyte layer forming step, the compressing step, and the dielectric layer repairing step are carried out in the stated order.
According to these methods, it is possible to produce an electrolytic capacitor that can be built in a circuit board, with a minimum of influences of stress to the electrolytic capacitor when the electrolytic capacitor is built in a circuit board.
An electrolytic-capacitor-containing circuit board of the present invention includes the electrolytic capacitor of the present invention.
Furthermore, in the electrolytic-capacitor-containing circuit board of the present invention, the electrolytic capacitor of the present invention may be embedded in an insulation material having a wire layer, and the electrode lead part of the valve metal element for an anode and the charge collecting element for a cathode may be connected individually with the wire layer. The insulation material preferably is a composite material containing inorganic material particles and a thermosetting resin.
This configuration of the foregoing electrolytic-capacitor-containing circuit board of the present invention allows the circuit board to be capable of high-frequency response and large-current driving.
Furthermore, an electrolytic-capacitor-containing circuit board producing method of the present invention includes the step of burying the electrolytic capacitor in the insulation material in a non-cured state by pressing, wherein a pressure in the burying step is smaller than a pressure applied to the capacitor forming part of the valve metal element for an anode of the electrolytic capacitor when it is compressed.
By the foregoing method, it is possible to build an electrolytic capacitor in a circuit board while suppressing occurrence of short circuits and an increase in leak current in the electrolytic capacitor.